In The Andalite Chronicles, Elfangor flees to Earth, permanently becomes a human, marries Loren, and fathers a son before the Ellimist returns him to his Andalite form and the StarSword.
In The Hork-Bajir Chronicles, Aldrea permanently morphs into a Hork-Bajir, marries Dak Hamee, and has Hork-Bajir children. When she "appears" in the main series (as a kind of psychic back-up-disk downloaded into Cassie's brain), this is the source of a lot of friction between her and Andalite team-member Ax.
Toomin in The Ellimist Chronicles with the Andalite cavemen.
To a degree, Edriss in Visser.
Also, Ax, to a degree. By the end of the series he's arguably more human than Andalite in terms of personality and habits.
This applies to the Chee as well after they used their holograms to disguise as humans.
In Arrivals from the Dark's Envoy from the Heavens, Trevelyan eventually learns that a researcher named Hugo Tasman, who is listed as MIA by the Foundation, has found a life for himself on the Medieval Stasis world of Osier, where he's made himself a nobleman and married a local woman. While he can never have children with her (these Human Aliens are incompatible with humans), he is still far happier here than back on Earth. Trevelyan agrees to keep his secret, and the Paraprims agree to allow Tasman to stay, as long he doesn't mess with the local culture.
In the Belisarius Series, Damodara begins to adopt Rajput ways in the realization that they were the best warriors that the Malwa Empire could field (except for the Kushans with whom they were roughly equal) and flattering them was a way to gain military success and not coincidentally gain the throne.
In George Orwell's early novel, Burmese Days, Flory admires Burmese culture more than he does his own, and despises the British Empire. It looks like he might be going this route, but the trope is subverted when he takes command of the police and breaks up a riot intent on destroying the Club and killing Ellis.
The literary critic V. S. Pritchett once described the period Orwell spent living as a tramp as "going native in his own country."
Jimbo in Cloud of Sparrows came to Japan from America as a Christian missionary; after being badly injured and subsequently rescued by a group of children, he ended up becoming a Buddhist monk who speaks fluent Japanese.
Ho Sa in the Conqueror books. When he first joins the Mongols in Lords of the Bow, he is initially reluctant, but later catches himself enjoying his new life. By Bones of the Hills, he doesn't want to go back.
A literal example occurs in the Ray Bradbury short story Dark They Were, and Golden-Eyed, about the first colony on Mars. The Martians all died out centuries ago, but as time goes on the colonists gradually change into Martians themselves and abandon the settlement, until a follow-up expedition sent to find the vanished colonists assumes they are a previously undiscovered native tribe.
Marion Zimmer Bradley's Darkover novels are full of Terran citizens going native on Darkover; Andrew Carr and Magdalen Lorne are notable examples. There are also Darkovans who try to go Terran.
In Deryni's King Kelson's Bride, Morag, Mahael and Teymuraz think that Liam-Lajos may have done this during his four years at Kelson's court in Gwynedd, making him unfit to rule Torenth. They discuss the possibility of passing over Liam in favour of his younger brother Ronal-Rurik.
Repeatedly Played for Laughs in Discworld, where many barbarian armies have tried to take over Ankh-Morpork. In a matter of months they are somewhat confused to find that their weapons and horses are now property of Ankh-Morpork merchants, and that they are now just another minority with their own fast-food places and gang graffiti.
In Rosemary Sutcliff's The Dolphin Ring's The Lantern Bearers, a young Roman's sister is kidnapped by the Saxons. Years later, he's captured in turn and finds her married to her kidnapper and mother to his son. She helps him escape, but refuses to go with him.
In Dune, protagonist Paul Atreides and his mother Lady Jessica, after being rescued by the desert-dwelling Fremen, are assimilated into the culture. Paul takes to it very strongly, and is a feared leader and eventually becomes the Fremen's messiah.
Eaters of the Dead features an Arab going native amongst Vikings. It's a rare example of an Eastern character going native amongst Westerners.
In Ecotopia, the main character, William Weston, a reporter from New York, goes to examine the environmentally friendly nation Ecotopia (formerly the northwestern US), but ends up deciding to stay there after he acclimates to the country.
In The Faded Sun: Shon'jir, Niun and Melein give Sten Duncan a choice: Go Native or die.
In the Foreigner (1994) novels, protagonist Bren Cameron is the representative of the human Lost Colony to the alien atevi on whose planet they live. When the humans in charge of the colony's government begin acting like complete morons he throws his lot in with the atevi, both to protect the atevi from being double crossed by the humans and to protect the human colony from the stupidity of their own government. The human electorate eventually wises up and replaces the morons with officials who welcome Bren back, but by that time he's become so deeply enmeshed in the fabric of atevi politics that he decides he can do everyone the most good by staying there.
The Ganymede Takeover by Philip K. Dick and Ray Nelson. An alien official is sent to rule over part of Vichy Earth, and is shocked to find his predecessor (also an alien) has become a Catholic and has a hobby of collecting model WWI airplanes.
In Dan Abnett's His Last Command from the series Gaunt's Ghosts, Gaunt's 'forced' Junior Commissar Ludd betrays his trust by reporting him in the eve of battle even though Gaunt fully expects him to do so.
Aziraphale and Crowley, an angel and a demon respectively, end up going native towards humanity as a result of having been on Earth since the very beginning. Neither are happy to learn about the imminent apocalypse and try their best to hamper its progress.
Adam ends up becoming an Anti-Anti-Christ as a result of this, refusing to start the apocalypse due to his time on Earth having left him neither evil nor divine, but fundamentally human.
In Guns of the Dawn, the armies of Lascanne and Denland are fighting through a swamp, and Mallen, the chief scout on the Lascanne side, has spent so long there that his sympathies lie more with the swamp's "indigines" than with either army. He helps his own side in the fight, but always in a way which doesn't conflict with his apparently higher priority of keeping the indigines out of harm's way.
In Ursula K. Le Guin's Hainish short story "Solitude", Ren, the daughter of a Hainish anthropologist doing fieldwork on the planet Eleven-Soro, goes spectacularly native after living for years in Sorovian society, such as it is. She chooses to remain there even after her mother and brother return to Hain, meaning that she'll never see them again.
Heart of Darkness by Joseph Conrad (which would later have a famous adaptation in the Vietnam movie Apocalypse Now). Kurtz is sent to Africa as an ivory-procurement agent and suffers a spectacular back story breakdown. The narrative either plays the trope straight or subverts it, depending on the reading, though the latter seems more likely. According to the first reading, Kurtz possibly goes native in horrifying ways, inverting the European life he came from. In the alternate reading, while he has shed his civilized persona, he still hasn't gone native in a meaningful way. Instead, an unnatural and immoral co-dependent relationship has formed, where the natives worship him as a god, while he in return treats them with utter ruthlessness, much like an unloving god would. The title of the paper Kurtz had been working on was "Suppression of Savage Customs": it is ended with the sentence, handwritten at a later date, "Exterminate all the Brutes!" Not quite the typical going native.
In The Heroes of Olympus, Jason Grace is initially one of the two praetors of New Rome. However, after getting forcibly relocated to the Greek Camp Half-Blood and falling in love with a Greek demigod, he finds himself torn between the two factions until he fully and officially chooses Greek in the fourth book. Conversely, Percy Jackson is forcibly relocated to New Rome, and after being made a member of the Legion in the wake of a massive battle, becomes more and more attracted to Rome, particularly the safe life he and his Love Interest could live there, protected by the Legion. He has not chosen Rome yet, but it seems likely he will at some point.
Stanislaus Grummann from His Dark Materials' The Subtle Knife spent the rest of his days as a Siberian shaman.
In Stephenie Meyer's adult novel The Host (2008), the alien invaders, the so-called Souls, are physically inserted into a host body and take control of the host's body. In the titular character's case, the host's mind is still present, and they both think inside Melanie's body, with the Soul eventually coming to identify with the humans around them and help them work against the Soul invasion. Later, the ragtag group of human survivors finally finds another group of survivors with their own dual-minded alien/human, who literally refers to the situation as "going native."
Jacob Wheeler does this in Into the West after marrying a Lakota woman. They and their children shift between Native and white society as the series progresses. Jacob's cousin, Naomi, also goes native when she marries a Cheyenne chief, Prairie Fire.
When last seen, he was living high up in the mountains of Haiti, wearing only a singlet, dirty white-drill trousers, grass sandals, and a long tan beard; very healthy and happy, occupying a one-room hut with a lovely native girl, practicing modern medicine and studying ancient voodoo.
Kydd: What Renzi does in the latter parts of Artemis on a Pacific island the crew visits. Luckily, Kydd is there to (literally) knock him out of it before the cannibalistic rival tribe of the islanders hosting them can get there.
In Francis Carsac's La Vermine du Lion (The Lion's Parasites), the protagonist is a geologist, who ends up growing fond of the primitive natives of a planet that has attracted the attention of a powerful interstellar corporation, seeking the planet's natural resources. The geologist ends up helping the locals force the Earth government to establish a quarantine around the planet, thus protecting it from exploitation.
One of the characters in The Laundry Filesis actually an Eldritch Abomination known as the Eater of Souls who was stuck in a human body and trained to pass as an Englishman. The ones doing the training ended up doing too good a job of it.
In the Liaden Universe books by Sharon Lee and Steve Miller, this is an occupational hazard for the Scouts, whose task of exploring new worlds often results in them spending long periods immersed in alien cultures. Many an experienced scout, even among those who resisted the temptation, has retained traits from a culture where he or she felt particularly at home.
Light And Dark The Awakening Of The Mageknight: Human Doug is so taken by elfin culture (and one member in particular) that he chooses to spend the school year studying abroad in the elfin capital. In the sequel, he'll likely come back with a penchant for very bland tea.
The Black Númenóreans who escaped the destruction of the island-realm often ended up living in cultures loyal to Mordor, and becoming their leaders. At least some of the Nazgûl belonged to this group of people, as did the Mouth of Sauron. note Black is used in the Black Magic sense, not a racial sense.
Also in the back story, one of the Kings of Gondor does this when sent as a prince to the ancestors of the Rohirrim. His son's ascension to the throne leads to civil war, and the death of most of the royal line (hastening the end of the line).
The Elven-Kings of Mirkwood (Oropher and later Thranduil) were originally Sindarin elves who came to the Woodland Realm after the sinking of the sub-continent Beleriand, and ended up adopting the more 'earthy' customs of the Sylvan elves, to the point that Thranduil's son Legolas identifies himself purely as a Sylvan elf.
The trope codifier, A Man Called Horse, is about a white man captured by Native Americans who eventually assimilates into their culture. It is taught in many grade school literature classes in the US.
One of the Night Huntress books has a minor example. A friend of Cat's asked her to find out what happened to a reporter of his that was investigating the existence of vampires. Turned out the woman in question had found a vampire, and subsequently fallen in love and was living with her.
In Princess Holy Aura this is how Stephen Russ plans to handle the problem of finding the rest of the Apocalypse Maidens.
Discussed in Red Harvest. Protagonist detective, The Continental Op, comes to city of Personville (also known as Poisonville) and soon in process of trying to rid the city of organized crime he becomes involved with several gangsters, kills many people directly and indirectly, and shoots a cop. In books probably most famous quote, when talking about it, he compares his situation of slowly becoming corrupted by the town to this trope.
This damned burg's getting me. If I don't get away soon I'll be going blood-simple like the natives.
One of the protagonists of Diane Duane's The Romulan Way is Terise Haleakala-LoBrutto, a Starfleet Deep Cover Agent tasked with improving the Federation's understanding of the secretive Romulans. By the end of the book she openly admits to Bones McCoy that she's come to love living on ch'Rihan, and refuses his offer to be extracted with him.
Author Cassie Edwards wrote over 100 bodice ripper romance novels, particularly the Savage series, all of which feature a white woman hooking up with a Native American man and adopting the ways of his tribe. And while she's the most prominent example, she's not the only author to employ this scenario.
In Seraphina Dragons are discouraged from this, and punished with a memory-wipe if evidence comes to the Censors.
John Blackthorne from James Clavell's Shogun is an English sailor shipwrecked in old Japan. Unlike his shipmates, he decides to learn the language and cultural skills needed to fit into the unfamiliar society, and eventually decides that it's preferable to the society he came from in a number of ways. He's no Mighty Whitey: he has a lot of difficulty learning the new ways, becomes only moderately competent, does not impress people, and is usually irrelevant.
Carrie in Lisanne Norman's Sholan Alliance novels. After bonding with Kusac and living on his world for a while, she goes native.
One visiting lead archeologist makes the mistake of comparing the Sholans to trash then following it up by pointing out Carrie's 'Gone Native' status.
Daenerys Targaryen, from the sedentary Westerosi culture, is married off to Khal Drogo, a warlord of the nomadic Dothraki people, in the hopes of reclaiming Westeros with a Dothraki army. Throughout the first book, she learns the language and customs of the Dothraki people, begins to dress in their style, and develops a fierce loyalty to her new husband. Her older brother Viserys doesn't fare as well, getting offended by Dany's suggestions that he exchange his finery for more practical Dothraki clothing and becoming deeply embittered when he realizes that his sister's assimilation has given her far greater credibility with the Dothraki than he will ever command.
Jon Snow is forced to do this to the wildlings, becoming a Fake Defector. Ultimately subverted, as he never becomes the mask, running off when faced with having to kill an innocent civilian.
Mance Rayder was raised among the Night's Watch, but abandoned the order and joined the wildlings after spending a few days with a wildling woman and tasting the freedom that they enjoy. He eventually becomes their king.
In the backstory, House Targaryen slowly assimilated themselves into Westerosi culture after Aegon's Conquest. They stopped worshipping Valyrian gods in favor of the Seven, ceased practicing slavery, married local Houses, and eventually came to see themselves as Westerosi instead of Essosi. This is a major reason of the difference of opinion between Viserys and Daenerys regarding their place in Westeros. Viserys grew up in King's Landing, so his crusade to retake the Iron Throne is largely driven by homesickness. Daenerys was born in Dragonstone but raised in Essos all her life, so she has no memories in Westeros to cling to. Although she has plans to contest the Iron Throne, she bases it more from her birthright rather than a personal desire. Some characters even question the feasibility of someone who never spent a single day in the Seven Kingdoms wanting to rule it, unless she sees herself as Aegon 2.0 (and even then, Aegon grew up in Dragonstone, so he had far more experiences in Westerosi politics than Daenerys).
Marat Lon in Star Trek: Mere Anarchy. A human scientist assigned to help restore the devastated planet Mestiko, he remains when a reactionary coup forces the Federation and other aliens off the planet. He disguises himself as a native, but doesn't do a very good job of blending in. Fortunately, he is discovered by native factions sympathetic to his cause, who instruct him in how to pass as a Mestiko resident. He transforms over time from an arrogant, somewhat patronizing outsider to someone with a deep concern for the Mestiko peoples. He takes a native name and the woman who helped educate him in the local culture becomes his wife.
Neta Efheny, in Brinkmanship, a Cardassian spy inserted into the Tzenkethi Department of the Outside as a low-grade worker. She comes to prefer the certainty that comes with knowing your place and your function, worrying about nothing but how to perform that function, free from the need to face any of the complications regarding identity or responsibility. She eventually accepts the mind-numbing contentment of a low-grade Tzenkethi and allows herself to be fully subsumed into their society.
Sand People occasionally use kidnapping to replenish their ranks, but on one occasion, a Jedi left the Order and willingly became a Tusken warlord. Sharad Hett's life is covered elsewhere in the saga, but had an impact on A'Yark, Hett's sister-in-law. In Star Wars: Kenobi she believes Ben could be another mighty warlord for her people, and tries to convince him to join them. Ben seriously considers the idea as a way to protect Luke Skywalker covertly.
Invoked by the Mandalorians. They are not so much a race as a culture, since the original Taung species died out well before their rise to galactic prominence. If there's a worthy fighter who follows their code, wears the armor, speaks the language, fights under Mandalore's banner, and an established Mandalorian adopts or marries them into the clans (and age/gender/species isn't a hindrance), then the adoptee is just as much a Mando as one born into it. They've been known to recruit orphans or captives, or to hold tournaments (like the Great Hunt) to find worthy recruits, and even a few Jedi traded their robes for bes'kar armor. They see this method as both the way to get the best warriors possible and to keep their culture alive, even though it's under constant threat from their love of war. As long as there is one Mando who can find, teach, and adopt (or sire/birth) an heir, the Mandalorians are still alive.
Amusingly inverted in Neil Gaiman's Sherlock Holmes pastiche, A Study in Emerald, where the Great Old Ones returned to Earth centuries ago, but instead of wiping us out or forcing us to adapt their ways, they assumed leadership in human terms. This resulted in a pseudo-Victorian world where most people lead entirely normal lives despite the fact most crowned heads of Europe have an unpleasant number of tentacles under them, and even consider their existence a blessing that makes the civilization possible at all.
On the planet Avalon in Technic History, this Humans and Ythrians Going Native with each other is a minor local tempest in a teapot. As relations between Humans and Ythrians on the planet are good it is usually less the disapproval of the other species, but simply uneasiness at mixing and worrying that those Going Native won't have time for their own.
In Sweetheart of the Song Tra Bong from The Things They Carried, Mary Anne Bell is the girlfriend of a young medic who falls in love with Vietnam and eventually crosses over to the other side, becoming part of the land.
In The Years of Rice and Salt, a Japanese ronin ends up with a Native American tribe and assimilates into their culture.
wrote over 100 bodice ripper romance novels, particularly the Savage series, all of which feature a white woman hooking up with a Native American man and adopting the ways of his tribe. And while she's the most prominent example, she's not the only author to employ this scenario.